Extract PRIME metadata in timeline export

<block ref="OBS">
   <metadata>
      <comment> Occultation by star HD157056 </comment>
      <comment>PRIME=JANUS</comment>
      <solarArrays>
         <fixedRotationAngle units="deg">-50</fixedRotationAngle>
      </solarArrays>
   </metadata>
   <startTime> 2032-07-02T04:18:40 </startTime>
   <endTime> 2032-07-02T04:32:00 </endTime>
   ...
</block>

now produce:

PTR_OBS_BLOCK,2032-07-02T04:18:40Z,2032-07-02T04:32:00Z,,JANUS

with export_timeline().

Changes

• Extract PRIME metadata from PTR as default source.
• Updated documentation to reflect the change.
• Added PTR snippet in the documentation for it to be compared with the output CSV.
• Fix pylint recursive option
• Fix documentation broken link
• Bump poetry dependencies and drop python 3.8 support ⚠.

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Closes #11 (closed)